Furnace



.April 26, 1932 N. R. DAvls 1,855,907

FURNAC E Filed Nov. 415, 1930 Ihvehtor Neville FL Davis,

H is Attorhe.

Patented pr. 26, 1932 UNITED STATES NEVILLE RYLAND DAVIS, F ASHTON-ON-MERSEY, ENGMND, ASSGIlS'B` TO GENERAL ELECTRIC COIPANY, A CBPORATION @1? NEW Fourteen Application led November 13, i930, Serial No. 495,449, and lndreat Britain November 26,1929.

My invention relates to furnaces, more particularly to electrical induction furnaces, and has for its object the, provision of improved means for grounding the furnace charge in 5 order to preclude the possibility of the charge attaining a high electrical potential, such as would result if the charge were to make electrical connection with a portion of the electrical heating circuit.

According to my invention an orifice is provided in the wall of the crucible or furnace chamber in which a metal plug is inserted so as to make contact with the charge in the chamber. The plug is connected to earth so that the charge is prevented from attaining an unduly high potential if for any reason it be electrically connected with part of the electric heating circuit. For example, if a crack develops in the crucible or lining of an inductionfurnace the charge when molten may penetrate the crack and make electrical contact with the inductor coil of the furnace in which case the charge immediately assumes a comparatively high potential and may therefore be a` source of danger to the furnace men or others. With the earthing connection of the present invention the charge is always connected to ground and cannot therefore attain a high potential.

This earthing or grounding plug may be maintained cool by means of a suitable circulating fluid, .such as water, as described and claimed in my Patent No. 1,833.739,l dated November 24, 1931. It has been found that if the plug be thus cooled. the metal in the furnace tends to remain solid around the top of the plug owing to the cooling of the latter and does not weld or make Ygood thermal contact with the plug although the electrical connection thereby formed is suicient to earth the charge.

As the plug does n ot make a good mechanical oint with the solid portion of the charge adjacent thereto it can readily be withdrawn from the orifice in the crucible or furnace lining for the purpose of tapping the furnace if 4desired'. On withdrawal of the plug that portion of the charge which is adjacent thereto and remained solid will melt and the fur nace discharges through the orifice.

'lillel plug may be maintained in position in the orifice by any suitable means such as a yoke with bolts or a pivoted bar adapted to be drawn in position to engage the external end of the plug and maintain the plug in place.

At times, it is possible that the grounding circuit might be interrupted or opened by reason or" the grounding plug, or if the plug be cooled, the solidied metal'about it,-be

coming coated with some material such as slag or part of the refractory material from the furnace. ln order to givenan indication that the plug is properly connected to the chargeql have provided suitable means for indicating an electrical condition in the grounding circuit. Preferably, two plugs will be provided, both of which will be arranged' to make contact with the furnace charge. These plugs will loe connected to form a local electric circuit a portion of which is constituted by the metal ot the charge. Connected to respond to an electrical condition in this local circuit is a suitable alarm device. So long as both the plugs make good electrical contact with the charge and the local circuit is completed no alarm signal will be given: or it desired an indication by means of a suitable lamp, for example. may be atlorded when the plugs are in condition for proper operation. lf., however. for any reason'either of the plugs becomes insulated from the charge. the local circuit will be in? terrunted' whereby the alarm signal is operated.

The local circuit may also be utilized to control the main heating circuit provided for the furnace so that in the event the local circuit be interrupted. as by the deposit of slag or like materi al. the main heating circuit will be opened. I eect this control by providing suitable cont-rolling means for effecting the opening of the circuit breaker or like controlling switching element provided for the heatingcoils in response to an interruption of the local circuit..

For a more complete understanding-of my invention reference should be had to the acv companying drawing in which the single diagrammatic ligure illustrates in vertical section an electrical induction furnace provided with a grounding circuit embodying my invention, the 4grounding circuit including a suitable alarm device, and also suitable means for controlling the induction heating coils provided for the furnace.

Referring to the drawing, I have shown my invention in one form in connection with an electrical induction furnace comprising Walls 10 delining a metal melting chamber 1,1, and a suitable induction coil or heating element 12. The walls 10 are provided with a pair of apertures 13 and 14 in which are inserted grounding plugs 15 and 16 respectively. It will be observed that these plugs roject suiciently far into the melting chambr to be in contact with the furnace charge 1 The plugs 15 and 16 are electrically connected together in a local circuit including the furnace charge 17, a suitable source of electromotive force 18, shown as a battery, and a suitable signal device 20, shown as an incandescent lamp. -This signal device instead of being of the visual type as shown may be of the audible type, it being understood that any suitable signal device which will give an indication when the local circuit is interrupted may be used. This local circuit is grounded, as indicated by the numeral 21.

It will be understood that so long as the local circuit remains closed or completed the signal lamp 20 will remain lighted indicating that the plugs are in good electrical contact with the furnace charge, and consequently that the charge is properly rounded. If for any reason either or both of the plugs become disconnected or insulated from the charge, as by a deposit of slag or other material. the lamp will be deenergized giving an indication that the local circuit has been opened.

If an audible signal be used instead of the lamp, it is preferable that the audible alarm be given in response to the interruption of the local grounding circuit.

In place of an alarm signal or in addition thereto, the interruption of the local circuit may be arranged through a relay device to operate some part of the main electric heating circuit of the furnace such as for example to cause a circuit breaker to open and thus interrupt the mainsupply to the furnace coil. As shown in the drawing, the induction coils 12 are supplied from a suitable source of electrical supply 22, a suitable circuit breaker 23 or like controlling switching element being included in the connections between the coils 12 and the source 22. The holding coil 24 provided for the circuit breaker 23 is energized continuously'by means of any suitable source of electrical supply 25, shown as a battery, as long as the local grounding cir cuit is maintained but is deenergiz'ed immedithe event the grounding circuit be opened. To effect this control of the holding coil 24, I provide a suitable relay 26 in the local grounding circuit, which relay as shown, is energized to closewhen the local circuit is completed, and is deenergized to open when ymaintain the energizing circuit for the induction coils 12. However, if for any reason the local grounding circuit be open-circuited, the relay 26 will open so as to effect a deenergization of the induction coils.

The plug or plugs may be arranged at any convenient part of the furnace but advantageously in or near the bottom, this being particularly useful when either of them 1s intended to be employed to close a tapping orifice, such as described and claimed in my above mentioned patent.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a metal melting furnace, a grounding circuit for the charge of said furnace and a signal device for indicating an electrical condition in said grounding circuit.

2. In an electrical metal melting furnace, means for grounding the charge in said furnace comprising a local circuit including said furnace charge and a signal device in said local circuit for indicating lan electrical condition in said circuit.

3. In an electrical metal melting furnace having walls defining a charge receiving chamber, means providing a local circuit including a portion of the furnace charge, a signal device in said local circuit for indicating an electrical condition therein and 4means grounding said local circuit.

4. In a metal melting furnace, means for preventing the furnace charge from attaining an electrical potential comprising a plurality of members in electrical contact with different portions of said furnace charge, electrical connections between said members whereby said members and said furnace I charge are connected in a local circuit, means 05 ately to allow the circuit 'breaker to open in grounding said electrical connections and a signal device for indicating an electrical condition in said local circuit.

5. In an electrical induction furnace, means for preventing the furnace charge from attaining an electrical potential comprising a plurality of members in electrical contact with diferent portions of said furnace charge, a source of electromotive force, electrical connections between said source and said members so that said members, said source and said furnace charge are connected in a.local circuit, a signal device in said local circuit arranged to give an indication when said circuit is interrupted and means grounding said local circuit.

6. In an electrical induction furnace provided With walls defining a metal melting chamber having a pair of apertures therein, metallic plug-like members projected through said apertures so as to be in electrical contact with the furnace charge, a source of electromotive force, a signal device, electrical connections including said source, said signal device, said plug-like members and said furnace charge in a local circuit, said signal device being arranged to give an indication in the event said local circuit is interrupted and means grounding said plug-like members.

7. In an electrical induction furnace having walls defining a metal melting chamber, means providing a local circuit including a ortion of the furnace charge, means grounding said local circuit and a controlled device operated in response to an interruption of said local circuit.

8. In an electrical furnace having Walls defining a metal melting'chamber and electrical heating means therefor, means providing a local circuit including a portion of the furnace charge, means grounding said local circuit, and-means dependent upon an electrical condition in said local circuit for controlling said heating means.

9. The combination'with an electrical induction furnace having walls defining a metal melting chamber, electrical induction heating coils for said chamber and an energizing circuit for said heating coils, of a pair of metallic plug-like members in said chamber walls in electrical contact with the furnace charge, electrical connections between said plug-like members providing a local circuit including said furnace charge, a source of electromotive force in said circuit, and a relayT in said local circuit connected to control said energizing circuit so as to eii'ect an interruption thereof in the event said local circuit is broken.

10. In an electrical induction furnace having Walls defining a metal melting chamber and induction heating coils for said melting chamber, means providing a local circuit including the furnace-charge, means grounding said local circuit, means for controlling said heating coils in response to an electrical 

